Common bottlenose dolphin in Slovenia and off Istria, Croatia

Common bottlenose dolphin in Slovenia and off Istria, CroatiaNatasa2016-05-29T14:07:18+00:00

Before looking deeper into common bottlenose dolphins (Tursios truncatus) in Slovenia and off the W coast of Istria, let us first introduce you to this interesting key species that has a significant role in maintaining the balance in a marine environment.

Mediterranean subpopulation

Bottlenose dolphins in the Mediterranean Sea are far spread. In the past, their distribution was more evenly spread in the overall range. Nowadays, due to the different and growing anthropogenic pressures, the distribution is patchy. The territory comprises coastal and offshore waters, with dolphins seen around many of the offshore islands.

Adriatic Sea

On the eastern side of the Adriatic there are subpopulation groups preferring certain areas (either south, middle or northern Adriatic). In between, there is a smaller density of dolphins due to multiple causes like less food availability, anthropogenic pressures and other specific habitat characteristics of the marine area. Fluctuations of individuals are present and Vivamar observes certain animals migrating in between them. This migration is good for gene flow.

Northeast Adriatic Sea

Bottlenose dolphins are regularly observed in the NE Adriatic Sea: Slovenia, Trieste Gulf, off west coast of Istria, southern most tip of Istria and in Cres-Lošinj Archipelago. Unfortunately, from three different species of dolphins that lived here in the past, this is the last constantly present marine mammal in the area.
There are different pressures posed on the local bottlenose dolphin population. These pressures have influenced their presence and distribution in the NE Adriatic. Animals seem to use areas linked to the prey availability more intensely and prefer areas that have less direct anthropogenic pressures, especially in the time of a calving period. For this, an archipelago-like coastline of the east Adriatic is very appropriate. Food availability is further connected to circadian and/or seasonal rhythms. A well known local example is when a large swarm of grey mullet (Mugil cephalus) enters the Slovenian sea in early spring which has been observed to be followed by dolphins. In such cases, bigger groups (aggregations) of dolphins might be seen in the area. Dolphin circadian mobility can show that especially in the summer months they move into deeper waters throughout the day, predictably to avoid man made activities that are more intense in daylight hours along the coast.

The taxonomy of the bottlenose dolphins is a bit unclear due to its geographical variation. There are several species of bottlenose dolphins, genus Tursiops, recognized.

There is also a subspecies of bottlenose dolphins in the Black Sea: Tursiops truncatus ponticus. This species is morphologically and genetically different from the ones we have in the Adriatic. The species that lives in the Adriatic Sea and is the the main subject of our research is the common bottlenose dolphin (Tursiops truncatus).